1. Field of the Invention
The present invention relates to a toner and a two-component developer each of which is used in an electrophotographic system, electrostatic recording system, electrostatic printing system, or toner jet system.
2. Description of the Related Art
Developing systems such as electrophotography are classified into a one-component developing system involving the use of toner alone and a two-component developing system involving the use of a mixture of a magnetic carrier and toner.
The two-component developing system provides a stable charging characteristic and is advantageous for maintaining high image quality over a long time period as compared to the one-component developing system because of the following reason: the two-component developing system involves the use of the magnetic carrier, and hence the triboelectric charging area of the magnetic carrier with respect to the toner can be widened. In addition, the two-component developing system is often used particularly in a high-speed machine because the magnetic carrier shows a high ability to feed the toner to a developing zone.
The surface characteristics of a toner particle have been known to affect various physical properties of toner such as charging performance. In view of the foregoing, the following contrivance has been conventionally made: the performance of the toner is improved by treating the surface of each particle of the toner. For example, a method involving mechanically smoothing the surface has been known (JP 02-87157 A and JP 07-181732 A).
However, an improvement in smoothness achieved by the mechanical surface treatment is still limited. A treatment with hot air has been known as another method to replace the treatment (JP 11-295929 A, JP 2003-162090 A, JP 2003-270856 A, and JP 2004-138691 A).
Although the treatment with hot air provides extremely high surface smoothness and improves the performance of the toner, the treatment is still susceptible to improvement in terms of a reduction in toner consumption and the prevention of toner scattering.
In addition, a spheroidized toner having a surface with its unevenness controlled has been known (JP 2004-246344 A).
Although such toner has achieved compatibility among charging performance, developing performance, and transferring performance, the toner still shows insufficient performance in terms of the prevention of scattering and dot reproducibility when applied to a high-speed machine.
A resin-coated magnetic carrier having an average particle diameter of 25 μm or more and 55 μm or less and a specified intensity of magnetization (JP 2002-91090 A) and a magnetic carrier having a volume magnetization of 20 emu/cm3 or more and 60 emu/cm3 or less (JP 09-281805 A) have been proposed as magnetic carriers used in two-component developers.
In each of those proposals, it is disclosed that the naps of a magnetic carrier on a developer carrying member are made dense so that dot reproducibility of electrostatic latent image on the image bearing member is improved, and excellent developing performance during a durability test under a normal-temperature, normal-humidity (having a temperature of 25° C. and a humidity of 50% RH) environment is achieved. However, each of the magnetic carriers is still susceptible to improvement in terms of the prevention of scattering, and developing performance and dot reproducibility at the time of a durability test under a high-temperature, high-humidity environment (having a temperature of 32.5° C. and a humidity of 80% RH).
As described above, various proposals have been made, but each of them is still susceptible to improvement in terms of a reduction in toner consumption, the prevention of scattering, and developing performance and dot reproducibility at the time of a durability test under a high-temperature, high-humidity environment (having a temperature of 32.5° C. and a humidity of 80% RH). Accordingly, a toner and a two-component developer each of which is capable of solving those problems have been demanded.